Obesity has reached epidemic proportions in the U.S. and plays a major role in the development of type 2 diabetes, dyslipidemia, and cardiovascular disease. There remains a very significant need for better non- surgical treatments. While most weight loss agents rely on suppressing appetite to reduce caloric intake, strategies that can safely enhance metabolic rate, a previously unrealized approach to weight loss or weight maintenance, have potential to effectively treat obesity. Brown adipocytes have an extremely high metabolic rate because they express mitochondrial uncoupling protein-1 (UCP1). This protein dissipates the electrochemical gradient in the mitochondria of brown adipocytes as heat. Brown adipose tissue (BAT) thermogenesis is increased upon exposure to low temperatures, and plays an important role in the maintenance of body temperature and energy balance in rodents. BAT is also a flexible tissue that normally enlarges or atrophies over time depending on environmental temperature. In many different rodent models, enhancement of BAT mass has convincingly been shown to lead to weight loss and diabetes resistance. While BAT was until recently thought to be effectively nonexistent in adult humans, recent data obtained with PET imaging shows that adults in fact have significant BAT, and that this tissue is functional. Other data demonstrates that the amount of active BAT in individuals is strongly correlated with leanness. Until recently no brown adipocyte stem cell had been identified. We discovered a population of human skeletal muscle-resident brown adipocyte progenitors that under appropriate conditions become fully functional brown adipocytes. Following differentiation, these cells have high levels of UCP1 and a very high metabolic rate. This unique human progenitor population can now be utilized to identify molecular actors involved in human brown adipogenesis. We believe that some of the mechanisms/targets of existing drugs and other compounds may be involved in brown adipogenesis, and our preliminary data demonstrates this on a small scale. Here we propose to develop a novel high content assay system and deploy it to screen a library of compounds with known targets and cellular mechanisms of action. In doing so we anticipate that this unique assay system may uncover targets previously unsuspected of being involved in brown adipocyte recruitment. This work could therefore provide important insights for directing future drug development aimed at increasing brown fat in humans. If this Phase I project is successful, we plan subsequently to further characterize mechanisms with practical potential for further development by determining their specificity for and contributions o brown adipogenesis. We will then identify more potent and specific compounds based on these findings and test the best compounds in animal models of obesity.